Pump applications using dry installed centrifugal pumps intend pump applications in which the liquid pumping centrifugal pump is not lowered into the liquid that the centrifugal pump is arranged to pump. Instead the centrifugal pump is arranged on the outside of the liquid holding tank, usually at the level of the bottom of the liquid holding tank. Furthermore, such a pump application require a suction pipe extending from the liquid holding tank to the inlet opening of the centrifugal pump.
In pump applications where the centrifugal pump is lowered into the liquid that shall be pumped there is usually not a problem to clean the inlet opening of the pump. The pump is hoisted and either the inlet opening is cleaned automatically upon hoisting due to gravity or the inlet opening is cleaned manually when the pump is lifted out of the liquid holding tank by flushing it with water or manually removing waste matter. In centrifugal pumps having a so called open impeller, when the pump is lifted out of the liquid holding tank, it is also easy to set and adjust the gap provided between the lower edge of the vane of the impeller and the impeller seat of the pump. Inspection and adjustment of this gap must be performed at recurrent interval due to the wear of the vane of the impeller and thereby the gap increase leading to deteriorating pump performance.
In pump applications where the centrifugal pump instead is dry installed, the inlet flange of the pump is bolted to a suction connection and in some applications the pump is supported by the suction connection and thereto a pressure pipe is bolted to the outlet flange of the pump. In other words, the hydraulic unit of the pump is very cumbersome to detach and in practice it is more or less fixedly arranged. Thereto the suction connection is bolted to a suction pipe that in its other end is connected to the liquid holding tank. The suction pipe is in almost all applications a conduit that sometimes comprises a maneuverable shut off valve that in its closed position prevents the liquid in the liquid holding tank to flow out when the pump is removed.
In order to clean the inlet opening of the pump and the impeller, the drive unit of the pump together with the impeller that is suspended by the drive shaft, have to be removed from the hydraulic unit of the pump. This is done by having straps and the like attached to the drive unit and thereafter a great number of bolts joining the drive unit and the hydraulic unit of the pump are loosened. Thereafter the drive unit is moved horizontally away from the hydraulic unit in order to expose the impeller. Upon adjustment of the abovementioned gap between the lower edge of the vane of the impeller and the impeller seat of the pump, so called trimming of the impeller, the impeller is displaced in the axial direction of the drive shaft of the drive unit in the direction away from the drive unit. This displacement is made with interest such that upon fitting in and reassemble of the drive unit the vane of the impeller abuts the impeller seat. Thereafter the maintenance staff measure the obtained distance between the real abutment surfaces of the drive unit and the hydraulic unit, whereupon the drive unit once more is lifted away from the hydraulic unit and the impeller is displaced in the axial direction along the drive shaft in the direction towards the drive unit the measured distance plus the predetermined height of the gap. Finally fitting in and reassembly of the drive unit takes place and then the maintenance staff may only inspect that the impeller runs freely and that the real abutment surfaces abut each other, and in other respects the maintenance staff has to rely on that the measuring and the trimming have been made in a satisfactory way. It shall be pointed out that a difference of the height of the gap by tenths of millimeters will affect the performance of the pump.
Today some suction connections comprises a small inspection hole, through which one with difficulty may introduce a mirror and see if the impeller and/or the inlet opening is clogged, in order to ensure that the drive unit is not unnecessarily detached and removed from the hydraulic unit. However, this inspection hole may neither be used to clean the impeller and/or the inlet opening, nor to trim and/or check the position of the impeller.